The present disclosure relates generally to patient access disconnection systems and methods for medical treatments. More specifically, the present disclosure relates to the detection of a patient access disconnection, such as the detection of needle or catheter dislodgment during dialysis therapy.
A variety of different medical treatments relate to the delivery of fluid to, through and/or from a patient, such as the delivery of blood between a patient and an extracorporeal system connected to the patient via a needle or needles inserted within the patient. For example, plasmapherisis, hemodialysis, hemofiltration and hemodiafiltration are all treatments that remove waste, toxins and excess water directly from the patient's blood. During these treatments, the patient is connected to an extracorporeal circuit and a machine, while the patient's blood is pumped through the circuit and machine. Waste, toxins and excess water are removed from the patient's blood, after which the blood is returned to the patient.
In the above treatments, needles or similar access devices are inserted into the patient's vascular system, so that the patient's blood can be transported to and from the extracorporeal machine. Traditional hemodialysis, hemofiltration and hemodiafiltration treatments can last several hours and are performed typically in treatment centers three or four times per week. In the in-center treatments, nurses monitor the patients to detect needle dislodgment. Nevertheless, a needle may not be in plain view of the patient or medical staff (e.g., it may be covered by a blanket) such that it is not readily visible.
Moreover, in view of the increased quality of life, observed reductions in both morbidity and mortality, and lower costs with respect to in-center treatments, a renewed interest has arisen for self-care and home treatments, such as home hemodialysis. Home treatments may be performed during the day, evening or nocturnally. If unsupervised or asleep, dislodgment risks increase because a caregiver is not present, while patient may not be aware of the dislodgment.
FIG. 1 illustrates a known access disconnection configuration. Blood is drawn from an arm 12 of a patient through an arterial line 14 connected to the patient via an arterial needle 14b. Blood is returned to patient 12 after it has been treated via a venous line 16 and venous needle 16b. Needles 14b and 16b connect to a shunt 12a, which is placed in fluid communication with one of the patient's veins. Accidental disconnection of the arterial line 14 during treatment is not as serious an issue because this situation simply eliminates the source of blood to the blood pump. Access disconnection of venous line 16 during treatment is a serious concern however because arterial line 14 keeps feeding blood to the blood pump, while venous line 16 returns blood to a location outside of patient 12.
Various systems exist for detecting needle dislodgement in hemodialysis. For example, U.S. Pat. No. 7,022,098 (“the '098 Patent”) and U.S. Pat. No. 7,052,480 (“the '480 Patent”), both entitled Access Disconnection Systems And Methods, and assigned to the assignee of the present application, disclose access disconnection systems that measure an electrical impedance of the extracorporeal dialysis circuit connected to the vascular access needles. An external voltage or current source injects a small current (e.g., less that 2.5 μ-Amp) into the blood flow. Measures are taken to ensure that the current does not exceed 10μ-Amp, which is considered in the art to be a safety limit for intercardiac devices. Such a small current however can be hard to detect. Further, impedance detection sensitivity may be decreased when the patient is connected by accident to earth ground.
Another problem with systems that inject current into the extracorporeal circuits occurs if the dislodged needle reestablishes contact with the other needle physically or through leaked blood. Here, the electrical parameter being sensed, e.g., impedance, may not change or not change enough to signal an access disconnection even though one has occurred.
A further obstacle involves the addition of electrical contacts to the disposable portion of the blood treatment system. Metal or otherwise conductive members placed in the disposable add manufacturing difficulty and cost.
A need accordingly exists for improved blood access disconnection systems.